1. Field of the Invention
This invention relates to an information transmission system which integrates various types of information equipment so as to make them function as a single system.
2. Description of the Related Art
Today, there is a flood of various types of information equipment on the market. They include personal computers, workstations, electronic notebooks, printers, copiers, electronic cameras, telephones, and facsimiles. Data exchange between such various types of information equipment is effective. The most common way to realize such data exchange is to connect various types of information apparatuses to each other through a LAN (local area network).
There arise various problems in introducing a LAN. They include: whether existing information apparatuses meet or can meet the requirements of a LAN; a LAN infrastructure must be prepared in advance; and data exchange cannot be performed between information apparatuses which differ in the method of handling data. If most of the existing information apparatuses cannot meet the LAN requirements, there is not much to be gained by introducing a LAN and therefore a LAN would not be introduced. Should the LAN be introduced forcibly, it would be necessary to introduce new types of LAN-compatible information equipment instead of the existing information apparatuses, resulting in an increase in the installation cost.
These days, information equipment of the portable type has suddenly been popularized and there have been demands for the use of this type of equipment on a LAN. Since providing for a function compatible with a LAN may hinder this type of equipment from being made portable, it is impossible to meet such demands sufficiently.
A simple method taking the place of the LAN is to use a floppy disk to mediate information between information apparatuses. This method, however, has several problems. They include slow writing/reading speeds, insufficient memory capacity, and the necessity of installing a driver in an information apparatus with a floppy-disk drive.
The ability to connect with communication equipment such as portable telephones is an important item for information transmission. Although the portable telephone is essentially designed to transmit and receive speech data, it can also transmit and receive such digital data as is recorded on a floppy disk. However, it is not practical to transmit and receive digital data by means of communication equipment such as portable telephones, taking into account transmission cost due to the circuit rental fee, an increase in the size of the unit resulting from the addition of a floppy-disk drive, and a decrease in the operating time due to the power consumption by the floppy-disk drive.
Recently, mediums with a large memory capacity such as optical disks or magnetic disks have been put to practical use and are finding wide application. The application includes data exchange as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 3-214310, which has disclosed a method of using a multimedia memory device with a storage medium of an optical disk as a common memory among different types of information apparatuses and realizing data exchange between the different types of information apparatuses via the multimedia memory device. Even this multimedia memory device, however, have a problem. As shown in FIG. 3 of Jpn. Pat. Appln. KOKAI Publication No. 3-214310, because the memory area of an optical disk is previously divided for each information apparatus, the capacity is exceeded at random for each memory area on account of the difference in the frequency of use of each information apparatus. In addition, since an information apparatus to be connected to the multimedia memory device is selected by operating a button on the panel PNL of FIG. 2 in Jpn. Pat. Appln. KOKAI Publication No. 3-214310, operation tends to be complicated. Furthermore, among the different types of information apparatuses, there is a combination of data-incompatible apparatuses. To make data exchangeable between such information apparatuses, it is necessary to provide the multimedia memory device with a data format converting function for making data exchangeable. This is troublesome. Since the multimedia memory device is shared by more than one information apparatus, there is no denying the possibility that entries to the multimedia memory device will overlap with each other and consequently there will be a waiting time before each entry is made.
An attempt to exchange data by means of IC cards intervening between various types of information apparatuses has been made recently. This attempt also has the following problem. A semiconductor memory device known as an SRAM is generally used as a memory built in an IC card. Thus, to prevent the information from being lost, it is necessary to incorporate a backup power supply in the IC card, making the card larger. When the built-in battery has run down, the important stored information is lost. To avoid this, the user has to replace the built-in battery periodically. Further, in order that the data sent from an information apparatus incompatible with the apparatus at the called party can be read by the latter, data-format information from an information apparatus at the calling party must be previously given to the information apparatus at the called party. This is troublesome.
Recently, nonvolatile semiconductor memory devices have appeared as an alternative to fixed magnetic disks. The fixed magnetic disk unit is provided with many functions for exchanging data with the CPU (central processing unit). When as many functions as there are with the fixed magnetic disk are given to the driver for nonvolatile semiconductor memory devices, an increase in the cost results.
With a conventional transmission method of connecting various types of information equipment to a transmission line such as a LAN and transmitting digital data of video or audio information between information apparatuses, data can be exchanged only between data-compatible information apparatuses, with the result that data transmission is restricted to a very limited range. There is another method of transmitting data via a magnetic recording medium. This method, however, has a portability problem, an information reliability problem, and a durability problem. In addition, the last method cannot be used between data-incompatible information apparatuses.